This disclosure relates in general to various embodiments of a belt support module and more specifically, to a flexible electrostatographic imaging member belt support module which reduces and/or suppresses belt rippling effects.
Flexible electrostatographic belt imaging members are well known in the art. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems; electroreceptors or flexible ionographic imaging members for electrographic imaging systems; and flexible intermediate transfer belts for transferring toner images in electrophotographic and electrographic imaging systems.
The flexible electrostatographic imaging members can be in the form of seamless or seamed belts or webs. Conventional flexible electrophotographic imaging member belts comprise a charge transport layer and a charge generating layer on one side of a supporting substrate layer and an anti-curl back coating applied to the opposite side of the supporting substrate layer to render flatness. Electrographic imaging member belts, however, may typically have a simpler material structure, including a dielectric imaging layer on one side of a supporting substrate and an anti-curl back coating on the opposite side of the substrate.
Additionally, flexible intermediate transfer belts are generally single layer semi-conductive substrate belts. The belts have a specific electrical conductivity to effect toner image transferring from photoreceptor surface onto the intermediate transfer belt.
Typical electrostatographic imaging member belts are seamed flexible belts. They are belts usually formed by cutting a rectangular sheet out from a production web stock, overlapping the two opposite ends, and joining the overlapped ends together to form a seamed belt. The fabricated seamed flexible belt is then mounted over and encircled a machine belt support module consisting of a plurality of belt support rollers of different diameters for use in an electrostatographic imaging machine.
While the scope of the embodiments of the present disclosure covers an improved belt support module design for enhancing flexible electrostatographic imaging member belt machine function, the following discussion will herein after focus, for reason of simplicity, only on flexible electrophotographic imaging member seamed belts preparation and their machine function as representation of the overall development.
Flexible electrophotographic imaging member belts can be multilayered photoreceptors used for a negatively charged electrophotographic imaging system. In such a system, the belts can comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, a charge transport layer, and an anti-curl backing layer. One type of multilayered photoreceptor belt comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. For example, U.S. Pat. No. 4,265,990, incorporated herein by reference in its entirety, discloses a layered photoreceptor having separate charge generating (photogenerating) and charge transport layers. The charge generating layer is capable of photogenerating electron-hole pairs and injecting the photogenerated holes into the charge transport layer.
The electrophotographic imaging members in the aforementioned system usually require an anti-curl back coating, applied to the back side of the supporting substrate opposite the electrically operative layers, for counteracting and balancing the curl to render imaging member flatness. This is because without the application of an anti-curl back coating, a flexible imaging member sheet, for example, about 16 inches (40.64 centimeters) in width by about 48 inches (121.9 centimeters) in length, will curl somewhat spontaneously upwardly into an about 1½ inch (38.1 millimeters) diameter roll. Although the application of the anti-curl back coating is solely for the mechanical purpose of maintaining the imaging member flatness, nonetheless the need of the anti-curl back coating will cause a substantial internal tensile strain (or stress) build-up in the charge transport layer as a consequence of counter-acting the upward curling effect.
After application of the anti-curl back coating, the prepared production electrophotographic imaging member web stock is then cut to give rectangular or parallelogram shape sheets of precisely predetermined dimensions. The opposite ends of each cut imaging member sheet are brought together to produce an overlap, such as a 1.0 mm overlap. This is followed by application of a joinder process, such as an ultrasonic welding process, along the overlapped region to form a seamed imaging member belt. The seamed imaging member belt is then mounted over and encircles a machine belt support module ready for electrophotographic imaging processes.
Although excellent toner images may be obtained with multilayered belt photoreceptors, it has however been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, the pre-mature onset of the formation of photoreceptor belt ripples or wrinkles along the longitudinal belt direction can occur. This is after, in some instances, a just few hundreds dynamic belt cyclic revolution around the belt support module during machine imaging function.
In this regard, it has been found during operation, that fatigue induced centric belt compression can be created by the dynamic imaging member belt cyclic motion. When the belt is cycled around the rollers during operation, compressive forces in the cross-web direction are generated. These forces cause compression from both of the parallel longitudinal edges of the belt directed toward the longitudinal center. This triggers the formation of fatigue induced wrinkles or ripples in the belt.
In a cross section viewing transversely at the photoreceptor belt, the above noted ripples resemble a sine wave having an average amplitude of about 7 micrometers with a frequency of periodicity of about 6 ripples per inch belt width, and appear to the naked eye as series of fine rings extending around the circumference of a typical photoreceptor belt. The formation of wave like topology of these ripples in the photoreceptor belt has been found to alter the distance (or gap) between the photoreceptor belt surface and the machine charging device(s). Consequently, the ripples impact charge density evenness on the belt surface.
Moreover, the wavelike topology of belt ripples prevents intimate and uniform contact between a receiving copy sheet and toner images carried on the surface of the photoreceptor belt during toner image transfer step to also adversely affect the toner transferring efficiency and thereby impact the quality of the final print. Since belt ripples in the photoreceptor belt developed as a result of dynamic belt motion do manifest themselves into print defects in the final copy print-outs, their appearance impacts the copy quality and thereby shortens the photoreceptor belt service life.
There is also a great need for long service life flexible belt photoreceptors in compact imaging machines that employ small diameter support rollers for photoreceptor belt systems operating in a very confined space. Small diameter support rollers are also highly desirable for simple, reliable copy paper stripping systems which utilize the beam strength of the copy paper to automatically remove copy paper sheets from the surface of photoreceptor belts after toner image transfer. Unfortunately, small diameter rollers, e.g. less than about 0.75 inch (19 mm) diameter, raise the threshold of mechanical performance criteria to such a high level that early emergence of photoreceptor belt ripples, exacerbated by the larger induced bending strain in the belt over this small diameter roller, can become unacceptable. This may negate the benefit that is realized by employing a small belt module support roller to provide the paper copy self stripping result.
Furthermore, when cycled in an electrophotographic imaging system employing a complex belt support design having an active steering roll to control belt walk, the internal strain generated within the photoreceptor layers by the dynamic belt revolution is aggravated by the belt shear stress as a result of the steering action by the active roll. This steering action has been found to be the cause that leads to spontaneous development of ripples in the photoreceptor belt even for a belt mounted over a belt support module without utilizing a small 19 mm diameter roller.
In addition to the ripples manifestation into copy print-out defects, the belt ripples have also been found to prevent the toner cleaning blade for making intimate physical contact with the belt surface to thereby significantly reduce the efficiency of the blade's cleaning function. This, in turn, is detrimental to the creation of high quality images in the final print copy. Moreover, belt ripples do also seem to prevent intimate cleaning contact with the photoreceptor belt surface for efficient cleaning.
Although the foregoing discussions are focused only in terms of dynamic mechanical interaction between an electrophotographic imaging belt and a belt support module leading to the development of belt ripples and cleaning issues, nevertheless the problems described and their respective solution are equally applicable to the electrographic imaging belts as well as the intermediate transfer belts.